This story has been updated to include comments from the Board of Elections.

STATEN ISLAND, N.Y. -- The votes haven't all been counted,
but Bill Thompson is stepping aside - the former comptroller ended his mayoral
campaign Monday with a City Hall steps endorsement of Bill de Blasio.

De Blasio finished at the top of the pack in the Democratic primary - but his
unofficial vote tally hovered around 40 percent, making it unclear if he had legally
avoided a run-off challenge from Thompson, his closest competitor.

And while as of Friday Thompson said he was in it for the
long haul - until all the votes were counted - he said Monday that it was clear
the vote count would take an unacceptably long time, making it impossible to
effectively campaign.

"It would be a disservice to my supporters, a disservice to Democrats,
and most of all, a disservice to the people of New York City who are desperate for
new direction after 12 long years," Thompson said.

He would not have dropped out, he said, if it were a general
election that determined who would ultimately be mayor. But he said in this
case he could step aside because he and de Blasio shared the same vision for
the city.

"Today I'm proud to stand next to a great New Yorker, and
throw my full support behind him. And I ask every single person who campaigned for
me supported me and voted for me to do the same thing," he said.

Among those Thompson supporters present at the unity press conference
was City Councilwoman Debi Rose (D-North Shore). Michael Mulgrew, the UFT
president, who resides on Staten Island, was also there. There were no traces of the sometimes
rough campaign - Thompson launched a website calling de Blasio "Bill de Bliar" -
during a press conference that saw them complimenting each other, along with
Gov. Andrew Cuomo, the state's highest ranking Democrat.

But there were harsh words - for the city's dysfunctional
Board of Elections. Thompson said every vote still needed to be counted - even
as he decided not to participate in the run-off.

"We're talking about tens of thousands of votes that's a
disgrace," he said. "In the greatest city in the world, in the greatest
democracy on earth, we ought to be able to count all the votes."

But the Board of Elections was defending its performance
Monday, blaming the delay in counting paper ballots on the law - which bars
them from counting those ballots earlier than Monday.

Spokeswoman Valerie Vazquez said board staff, in the
presence of the campaign, began canvassing paper ballots at 10 a.m. Monday.

"We could not open up any paper ballots ... until today,
especially for the fact that we can continue to receive absentee ballots," she
said.

In the terms of affidavit paper ballots, the board must
determine those people rightfully swore they were properly registered to vote
in a party primary, she said.

"The board staff has to do their due diligence and confirm
that's the case," she said. "And then Monday, today is when we start canvassing
those ballots."

De Blasio praised his one-time opponent as a man of integrity
to whom he would would go for advice and counsel if he is elected mayor.

"I am profoundly honored. I am profoundly humbled to receive the
support of Bill Thompson and his extraordinary coalition," de Blasio said. "It means
so much that we will be working in partnership for the good of New York City."

Cuomo told the crowd the city has primaries because people
have different ideas on how to accomplish their shared vision.

"What Bill Thompson is saying today is he's going to put
aside his own personal ambitions, his own personal hopes, his own personal
ideas, in honor and respect of that shared vision," Cuomo said. "It can be much
harder to step back than to step forward."

He also heaped praise on his longtime friend de Blasio,
with whom he worked in the Clinton administration - and took shots at
Republicans while he was at it, reminding the crowd that the GOP sought to ax
the Department of Housing and Urban Development.

"They believed the department was Mission: Impossible. You
can't provide affordable housing, and they believe that you can't help
struggling cities and you can't help the homeless and you can't empower people,"
he said. "And we said they were wrong."

He took a chance to outline his party's platform as the
mayoral race officially kicked into general election season, calling for
affordable housing, safe and clean public housing, sensible gun laws, and a
strong economy.

"This city sent a clear message to the rest of the country that
says we are not afraid of differences among us. We don't turn differences away --
we welcome difference," he said. "While other places are putting up walls to
keep people out, we open our arms and we keep people in."